The present invention relates generally to fasteners and, more particularly, to fasteners for securing structures to a rock, coral, or sandy-bottom seafloor. The present invention is especially directed to seafloor attachment bolts for securing split pipe armor for underwater cables to the seafloor.
U.S. Pat. Nos. 4,026,184 and 4,056,037 illustrate expansion-type anchor bolts which are similar to those commonly used for attaching structures to the seafloor. In the typical expansion-type anchor bolt, the shaft has a frusto-conically shaped end for insertion into a predrilled borehole and a threaded end. A collar is loosely disposed around the shaft above the frusto-conically shaped end. When a nut is tightened on the threaded end, the shaft is withdrawn from the borehole relative to the collar. The resulting movement of the frusto-conically shaped end into the collar spreads and expands the collar against the side of the borehole thereby holding the bolt in place.
The prior art expansion-type anchor bolt has two main disadvantages when used with subsea piping systems, both being related to the threaded bolt/nut installation technique. First, the installation requires a torquing device such as a wrench which is not easily manipulated by a diver. Second, threaded connections are subject to vibration loosening caused by subsea wave action. The life expectancy of the subsea pipe system in which the anchor bolts may be used is 20 years. Threaded fasteners usually vibrate loose within a year after installation in such an environment. There is therefore a need for a seafloor attachment bolt which may be easily installed by divers and which will not be loosened by subsea wave action.
In the art of blind fasteners, a push-pull installation technique is often used in joining a plurality of sheets together as exemplified by U.S. Pat. No. 3,792,933. Typically, a rivet is inserted through apertures in the sheets so that the head of the rivet seats adjacent one side of the sheets. Through the use of a special tool, a pushing force is applied to swage a malleable collar to a threaded or grooved portion of the rivet on the other side of the sheets. At the same time, a pulling force is applied to the rivet to pull the sheets tightly together.